Witnesses saw Charles “Butch” Walker, 33, holding the child near the water at 10 a.m. and called 911. Cops learned Walker had fled his nearby Clifton home after slashing the face of his ex-girlfriend, the baby’s mom.

Finding him at the water’s edge, Sheehey yelled, “Stop! Don’t move!” Walker plunged in – as did Sheehey, who grabbed the baby as the tot floated free of his dad’s arms.

Walker’s body was later fished out. Cops said his girlfriend had left the father of six last month.

Mother and child were in stable condition last night at St. Vincent’s Hospital.

As for Susan Sheehey, 32, who’s due Nov. 1, she breathed a sigh of relief.

“When they call you to the office, it’s scary,” said the PS 58 third-grade teacher. “But [then] I found out he was a hero.”